线程中互斥锁使用的步骤与信号量相似!
1、首先定义互斥锁变量,并初始化
pthread_mutex_t mutex_lock;
pthread_mutex_init(&mutex_lock,NULL);
2、在操作前对互斥量进行加锁操作
pthread_mutex_lock(&mutex_lock);
3、操作完毕后进行解锁操作
pthread_mutex_unlock(&mutex_lock);
所有操作均在加锁和解锁操作之间进行,保证同时仅仅对有一个操作对关键变量或是区域进行操作。
下面是自己写的一个小程序,对主函数对变量自加操作,而线程函数进行自减操作。
(该程序有个小bug,看官可执行运行一下,就知道结果了,高手一看就知道问题在哪里,哈哈!卖个关子!)
pthread_mutex_lock(&mutex_lock);对某个互斥锁变量进行加锁操作时,当该变量已经被另外一个线程锁住时,该线程会被阻塞(英文原文为block),可以理解为休眠。
由操作系统基本原理可知,当进程处于就绪状态时,才会获得处理机的时间片,换句话说就是能能被调度到处理机上执行,而阻塞状态则不能。
因此一个线程被阻塞后,将不会执行,处于等待状态,通常是等待某个事件发生或到来。因此,一个对已经加锁的变量进行加锁的线程将被阻塞,其只能等待另外一个线程解锁,才能继续执行。
1 #include<stdio.h> 2 #include<unistd.h> 3 #include<stdlib.h> 4 #include<pthread.h> 5 #include<string.h> 6 #include<errno.h> 7 8 void *thread_function(void *arg); 9 pthread_mutex_t mutex_lock; 10 int globaltmp=0; 11 int main(){ 12 int res; 13 pthread_t pthread_tmp; 14 pthread_mutex_init(&mutex_lock,NULL); 15 pthread_mutex_lock(&mutex_lock); 16 res = pthread_create(&pthread_tmp,NULL,thread_function,NULL); 17 if(res != 0){ 18 perror("thread creation failed!"); 19 exit(EXIT_FAILURE); 20 } 21 while(1){ 22 pthread_mutex_unlock(&mutex_lock); 23 sleep(2); 24 globaltmp++; 25 printf("in the main func,globaltmp=%d\n",globaltmp); 26 res = pthread_mutex_lock(&mutex_lock); 27 // if(res == EDEADLK) 28 { 29 // printf("it has been locked in the thread!\n"); 30 } 31 // printf(" main func res =%d\n",res); 32 sleep(2); 33 } 34 res = pthread_join(pthread_tmp,NULL); 35 if(res != 0 ){ 36 perror("thread join is failure"); 37 exit(EXIT_FAILURE); 38 } 39 printf("thread joined!\n"); 40 pthread_mutex_destroy(&mutex_lock); 41 return 0; 42 } 43 void *thread_function(void *arg){ 44 int res ; 45 res = pthread_mutex_lock(&mutex_lock); 46 if(res == EDEADLK) 47 printf("it has been locked in the main!\n"); 48 while(1) 49 { 50 pthread_mutex_unlock(&mutex_lock); 51 sleep(1); 52 globaltmp--; 53 printf("in the pthread func,globaltmp=%d\n",globaltmp); 54 // printf("I am in the pthread func\n"); 55 res = pthread_mutex_lock(&mutex_lock); 56 // printf("thread func res=%d\n",res); 57 // if(res == EDEADLK) 58 // printf("it has been locked in the main!\n"); 59 sleep(1); 60 } 61 pthread_exit(NULL); 62 }